Dynamically retrieve API spec yaml file from release asset

[zelinh]

Description

Currently we are storing the API spec yaml file within opensearch-build repo. With more changes happened in opensearch-api-specification repo, it's hard to maintain and update each time.
For smoke tests, this PR is to dynamically download the API spec yaml file from opensearch-api-specification pre-release asset.

If downloading fails, use the existing spec file from build repo.

Issues Resolved

#5239

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.04%. Comparing base (f502e9d) to head (22a5cc2).
Report is 16 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5305      +/-   ##
==========================================
- Coverage   92.06%   92.04%   -0.03%     
==========================================
  Files         202      202              
  Lines        7017     7036      +19     
==========================================
+ Hits         6460     6476      +16     
- Misses        557      560       +3     

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